Substantial energy savings are expected from changes being made to Dorchester's Corn Exchange building.

They are now likely to be higher than expected when the project began – due to the recent big increases in gas and oil prices.

The alterations include fitting a biomass boiler for central heating, low energy lighting and refrigeration and solar panels on the roof.

The changes come as part of a £2million revamp by Dorchester Town Council.

Exact savings have yet to be calculated but the use of the solar panels alone should generate around 25 per cent, or more, of the building's electricity needs.

Additional panels have just been agreed for the rear roof on the North Square side of the complex.

The town council is to use two additional roof slopes where they are unlikely to be seen from street level.

Sixteen extra panels are being planned in addition to the 52 already agreed for the main roof, which between them will generate 17,000kwh of electricity each year – a significant contribution to the 80,000kwh the complex was consuming before recent works to help make the building more energy efficient.

The listed Grade II building, dating from the mid-1840s, is said to be of "high architectural" interest and a significant feature in the town centre.

An application to Dorset Council from Crickmay Stark Architects on behalf of the council said that the additional panels will be added to a modern extension of the building and will be difficult to see from any angle: "The roof slopes are only visible from the adjacent roofs with a small glimpse of a distant view from Friary Lane," said a report with the planning request.

Other works already undertaken during the council's refurbishment of the Corn Exchange complex, also known as the Municipal Buildings, include new LED lighting, improved insulation and the replacement of about 65 per cent of the roof which was coming to the end of its life; more efficient refrigeration and conversion of the heating system to bio-mass, all part of the town council's commitment to climate change and future-proofing the building.

The biomass boiler, when operational, should have the capacity for excess power to be shared with neighbouring buildings.

Dorchester Town Council say it has insulated the small spaces in the roof with Welsh mountain sheep wool, which has been used to insulate the roof of the Corn Exchange and council chamber, while a mechanical, which has high insulation values and has also added a ventilation heat recovery system and destratification fans to recapture hot air escaping to the high roofs of the building.

Future proposals include moving staff out of their North Square offices and into an extension currently under construction at the rear of the Corn Exchange, which will be shared with Dorchester Arts. The existing town council offices, further down North Square, will then be sold, probably for housing.

The town council has committed to being carbon neutral by 2030, 20 years earlier than the Government target, and was one of the first Dorset councils to switch much of its outdoor machinery and two vans to electric power.

The town council say it has been putting money aside for years for the repair and maintenance works to the Corn Exchange building with the cost of the boiler and some of the other energy works part-funded by grant aid and government incentives.

The council says the carbon reduction measures total around £500,000, funded by the council (£200,000) a grant from Low Carbon Dorset (£200,000) and future Government Renewable Heat Incentive payments and other grants (£100,000).

When the project was agreed it had been calculated that the overall costs would be achieved through savings in 15 years after which there would be an ongoing financial benefit to council taxpayers.

Said town clerk Adrian Stuart: "Two years ago the buildings had a combined gas and electric budget of £22,000 a year. It was our expectation that the future cost of woodchip and electricity would be marginally lower, but the recent fuel price increases mean we may be protected from significant increases in fossil fuel energy prices."

But he says the financial equation was never the driver for this scheme, although it offers obvious benefits, more so since the rise in gas and oil prices.

"In 2019 when we declared a climate emergency the Municipal Buildings and 19 North Square combined represented a usage of 118t of CO2 a year, just under 80 per cent of all of our direct fossil fuel consumption. While in future our high-ceilinged, single glazed Victorian building may still consume a significant amount of electricity we would hope to reduce our overall carbon impact on this building by around 75 per cent, making the goal of reaching a net zero direct fossil fuel consumption at Council level ahead of 2030 a real possibility."

Mr Stuart says the council will now be looking to share the knowledge gained from the changes with operators of similar buildings that have traditionally been very carbon heavy.